Field of the Invention
The present invention relates to a lead frame structure, particularly a composite structure of flex substrate and lead frame suitable for the flip chip or wire bonding packaging process of LED and also semiconductor IC packaging process.
Brief Description of the Prior Art
A general flex substrate is made of copper foil and Polyimide, PI stacked together. Electric circuitry shall be formed by etching process and plating process to complete a flex substrate. Referring to FIG. 1 which shows an illustrative sectional view of a general flex substrate, the flex substrate 8 mainly comprises a flex base material 80, an upper metal layer 81 and an adhesive layer 82. A plating layer 83 is formed on top of the upper metal layer 81. During the manufacturing process of having an IC 84 eutectic using the flex substrate 8, a carrier (not show in the figure) must be used to enhance the mechanical strength of the flex substrate 8 and also improve the yield rate of IC packaging process. It is noted that the heat conductive coefficient of the flex base material 81 being approximately 0.1-0.35 W/mK which is very much lower than the heat conductive coefficient 398 W/mK of a copper metal lead frame.
A conventional lead frame is shown in FIG. 2 which is an illustrative sectional view of the same. The lead frame 9 comprises conductive leads 90 which having plating layers 91 formed on the upper and lower surfaces thereof. Because of the thickness of the lead frame 9 usually greater than the flex substrate, conductive leads space of lead frame greater than conductive lead space of the flex substrate, it results the number of the conductive leads of the lead frame 9 much less than the number of conductive leads of the flex substrate. Therefore, the dimension of resulted IC after packaging process becomes relatively large.